This invention relates to a process for making a soybean beverage base such as soy milk or food products made therefrom.
The use of soybeans as a protein source in foods is well-known. In spite of their high protein content, marketing of soybean products has had limited success primarily due to an objectional flavor described as "beany flavor." This objectional flavor is not present in the original intact, whole soybeans, but develops immediately after maceration of the bean. The beany flavor is believed to result from the lipid oxidation by lipoxygenase (formerly known as lipoxidase). This undesirable oxidative reaction is accelerated in a liquid medium, especially in the presence of water.
Conventional processes for preparing soybean milk include the step of soaking the soybeans in water for many hours and then grinding the beans in water to dissolve or suspend the proteinaceous and other components in the aqueous medium. The suspension or slurry thereby obtained is filtered to remove undesirable large particles and the filtrate is heated. The resultant product is high in protein content. However, as the soaking time for soybeans increases (for example, overnight), larger quantities of water-soluble solids leak out from the beans into the soak water, which is discarded in the conventional methods and that disclosed in U.S. Pat. No. 3,901,978. Analysis of the dry solids found in the soak water showed the following composition: 23.3% crude protein, 2.8% fat, 0.5% sucrose and 63.7% other carbohydrates.
Soaking of soybeans is a necessary and important step in the previous inventions. Therefore, the burden of nutritional loss, microbial growth, space requirement and investment cost which are associated with soaking processes would be lifted if the soaking step was eliminated. It also has been proposed in U.S. Pat. No. 3,901,978, issued Aug. 26, 1975, to prepare soybean milk by a process whereby the lipoxygenase is inactivated in the intact soybean. In this process, the intact soybean is tenderized in an aqueous solution, preferably an alkaline solution for several hours. The intact tenderized soybean then is heated at a temperature and for a time sufficient to inactivate the lipoxygenase enzyme. The beans then are ground in water and the slurry is homogenized. The soybean beverage is characterized by a reduced but still distinct beany flavor. However, in this new process and more traditional processes of soymilk production, soybeans are soaked before grinding.
It would be highly desirable to provide a process for making soybean beverages which contain substantially the same protein content as the soybeans and which are substantially free of beany flavor. Furthermore, it would be desirable to provide such a process which provides a soybean beverage which has good mouth feel, digestibility and homogeneity.